In women, two of the most widely used screening tests are the Papanicolaou (PAP) test to detect cervical cancer and mammography to detect breast cancer. Both screening tests have been successful in reducing the death rates from these cancer in certain age groups. There are still many cases that are not detected through these techniques and the mortality rate is very high due to high cost, lack of insurance coverage and reluctance.
In the case of breast cancer, great efforts have been made to develop a detection test by mammography. Although several studies indicate that mass mammography may be a useful strategy to reduce breast cancer mortality, this method involves a certain number of disadvantages. Some of the disadvantages are a high rate of false positives, frequent false negatives and enormous public health costs. Thus, when the benefits are weighed against these advantages, it is not surprising that this form of screening has engendered contentious debates over the last twenty 30 years.
In men, prostate-specific antigen (PSA) levels in the blood may be used to screen for prostate cancer. PSA levels are high in men with prostate cancer, but levels also are elevated in men with noncancerous (benign) enlargement of the prostate. Currently the main drawback to its use as a screening test is the large number of false-positive results, which generally lead to more invasive tests.
It is known that diagnosis and follow up of the evolution of cancer are carried out, besides direct observation of the tumors, by biopsy analysis or in the case of blood malignancies by analysis of the bone marrow, which implies either a surgical intervention, or an invasive test such as a biopsy or a bone marrow aspiration. Now, in addition to the disagreeable or even dangerous aspect of such methods, it has been observed that they may not be very precise. Current methods for classifying human malignancies are mostly to rely on a variety of morphological, clinical and molecular variables. Despite recent progress, there are still many uncertainties in diagnosis. Furthermore, it is likely that the existing classes of the tumors are heterogeneous and comprise diseases that are molecularly distant.